The major goals of this research is a molecular description of the constitutive heterochromatin of Drosophila melanogaster. We intend to purify heterochromatic DNA by molecular cloning in hybrid bacterial plasmids and to arrange each sequence in order along the chromosomal DNA. We are particularly intrested in characterizing the DNA of the pairing regions on the X and Y chromosomes which are adjacent and proximal to the nucleolus organizer. The bulk of the DNA of these regions is known to consist of tandemly-repeated satellite DNA. We shall separate and sequence the several distinct DNA species present with the satellites of Drosophila melanogaster. We hope to find stringent hybridization conditions which will allow us to localize each sequence by in situ hybridization conditions which will allow us to localize each sequence by in situ hybridization to mitotic chromosomes. We propose to use fluorescent dyes which stain specific regions of heterochromatin as an assay to detect and purify blocks of heterochromatin from Drosophila nuclei. We shall also use our knowledge of restriction sites in heterochromatic DNA in order to purify nucleosomes from specific chromosomal regions. In these two ways we hope to purify nucleosomes from specific chromosomal regions. In these two ways we hope to purify heterochromatin containing a single simple-sequence DNA in order to compare early embryo prior to heterochromatization with satellite chromatin of the blastoderm stage to determine what molecules or molecular forces are essential for the more condensed and more highly ordered state of heterochromatin.